Bacteria carrying plasmid having temperature dependent plasmid copy number

Abstract

Gene products of plasmid DNA, such as proteins, are prepared in high yields by cultivating bacteria carrying a plasmid which shows a controlled constant plasmid copy number at one temperature and a much higher or totally uncontrolled copy number at a different temperature. The plasmid may be prepared by recombinant DNA technique using a cloning vector showing the temperature dependent plasmid copy number pattern.

We claim: 
     
       1. A bacterium carrying a recombined DNA plasmid showing a controlled constant plasmid copy number when the bacterium is cultivated at one temperature, and showing, when the bacterium is grown at a different temperature, an altered plasmid copy number control allowing an at least 20 times higher or totally uncontrolled copy number. 
     
     
       2. A bacterium as claimed in claim 1 which is a mesophilic bacterium and wherein the plasmid shows a controlled constant plasmid copy number at temperatures up to 32° C., and an altered plasmid copy number control allowing an at least 20 times higher or totally uncontrolled copy number at temperatures above 36° C. 
     
     
       3. A bacterium as claimed in claim 2 which is an Escherichia coli. 
     
     
       4. A bacterium as claimed in any of claims 1 to 3, wherein the plasmid is a mini-plasmid. 
     
     
       5. A bacterium as claimed in claim 1, wherein the plasmid is a derivative of R1.